a) Field of the Invention
The present invention relates to an infinitely variable drive pulley for a belt drive transmission.
b) Description of the Prior Art
Pulleys of this type are known, and comprise opposed frusto-conical flanges which co-operate with a drive belt. Cone pulley is secured axially on the shaft and the other can be moved axially against the force of a return spring, by centrifugal weights in the form of adjusting levers that act on an adjusting stop through a cam surface and which are each supported so as to be able to pivot outwards about a pin that extends transversely to the shaft and is spaced radially therefrom.
To establish the size of the V-gap between the two pulley flanges of such drive transmissions as a function of the particular rotational speed, it is known (from US-PS 3 759 111) that levers acting as centrifugal weights can be associated with the axially adjustable pulley flange, these levers being supported on rollers associated with the fixed flange, so that when the adjusting levers pivot outwards as a result of centrifugal force the axially moveable flange is pressed towards the fixed flange. The axial adjustment path of the pulley thus depends on the angle to which the adjusting levers are pivoted, which in turn is determined by centrifugal forces and by the shape of the rolling track for the rollers on the adjusting levers. Thus, for a given course of the return force, a desired inter relationship of the axial movement of the movable flange and the rotational speed can be achieved by the shape of the rolling track of the adjusting lever (which forms a cam surface) and by the mass of the centrifugal weight formed by the adjusting lever, and the position of the centre of gravity of such mass. However, a given relationship between the axial movement of the moveable flange and the rotational speed can only be maintained if the position of the cam surface of the adjusting lever and the mass of the centrifugal weights and the position of the centre of gravity of such weights can be kept within close tolerances; it is extremely difficult to guarantee this in components made by production, and requires subsequent adjustment work.
It is known that to adjust the weighted levers, the position of each lever or of the roller that is associated with it as an adjustable abutment can be moved. However, such a step provides a corresponding matching potential and adjustment only in the range of small adjustment paths but not, however, in the range of larger adjustment paths, for which a match would be of considerably greater importance.